It is important that a driver, when driving a vehicle, check the circumstances of the vehicle surroundings, for example, for the existence or approach toward the vehicle of a person, other objects, or the like. In recent years, there have been implemented driving support devices and vehicle surroundings monitoring devices, in which a camera is installed in the vehicle and captured images are displayed on an on-board monitor device, whereby such a check is assisted. Sensors using ultrasound, radar, or the like are used to detect persons or objects approaching the vehicle in the vehicle surroundings. Also known is a technology for differentiating between stationary objects and moving objects and recognizing moving objects by image processing.
The principle of optical flow is often applied to moving object recognition employing image processing. For example, U.S. Pat. No. 5,777,690 (PTL 1) discloses a technology for analyzing temporal position changes of the vanishing point of the optical flow (the “focus of expansion,” or FOE), the appearance of a moving object being detected when the position changes a predetermined amount or more (column 7, line 58 to column 8, line 27, et al.). JP 2005-123968A (PTL 2) discloses a technology for providing a driver with notifications on the basis of the results of detection using optical flow, by providing a box around a moving object in an image or by emitting a warning sound or audio message ([0013] to [0019], and so forth).
Indicating in an image or emitting a warning sound or audio message to notify the driver of the presence of a moving object or the approach thereof toward their vehicle is likely to cause the driver to feel hassled. The driver may also feel hassled in cases in which the presence of a moving object or approach thereof toward their vehicle is detected in error. The monitor device or the like provided onboard the vehicle, although assuredly intended to assist with driving, is preferably used expressly for assistance purposes. It is desirable for the driver, when driving, to perform a check using his own five senses, and particularly by direct visual contact.